The present invention relates a novel amino-polyether-modified epoxy and an electrodeposition paint composition containing the same.
In order to protect metal materials from corrosion and keep their good appearance during using, they are provided with coating on the surfaces. Especially, as electrodeposition coating can simply and speedy form uniform coatings on surfaces of metal materials, it is industrially and widely used for coating metal materials having large surfaces to be coated, such as automobile bodies.
In an electrodeposited coating used in an automobile body, enhancement of adhesion with a substrate, an intermediate-coated or a top-coated coating provided on the substrate as well as enhancement of flexibility for improving chipping resistance are especially desired. Various compounds and resins are used to provide an electrodeposited coating with the flexibility.
For example, Japanese Laid-Open Patent Application Nos. 59-117560 and 6-87947 describe a cationic electrodeposition paint composition which contains a reaction product of polyepoxide with polyoxyalkylene amine.
However, when this reaction product is used as a component of a cationic electrodeposition paint composition, flexibility can be provided, but it adversely reduces adhesion with a substrate, an intermediate-coated or a top-coated coating provided on the substrate decreases.
Lately, it is strongly desired that an amount of solvent exhausted into air decrease, from a point of view of global environment, especially prevention of air pollution.
The present invention solves the problems as mentioned above and an object of the present invention is to provide a novel amino-polyether-modified epoxy and a cationic electrodeposition paint composition using the same as a flexible resin, so as to impart flexibility to an electrodeposited coating, with keeping adhesion with a substrate, an intermediate-coated or a top-coated coating as well as to decrease an amount of solvent used in electrodeposition paint in comparison with conventional one.
The present invention is a novel amino-polyether-modified epoxy obtained by reacting amino polyether represented by a formula as follow: 
wherein m is an integer of 2 or more, R is hydrogen, methyl group or ethyl group, and n is 2 or 3,
with polyglycidyl ether having a molecular weight of 1,000 to 7,000 and an epoxy equivalent of 500 to 3,500, wherein an equivalent ratio of a primary amino group of the above amino polyether to an epoxy group of the above polyglycidyl ether is controlled within the range of 0.52 to 1.0.
In the above formula of the amino polyether, one example is that, m is an integer from 5 to 25, R is methyl group, and n is 2. It is preferred that a molecular weight of the amino-polyether-modified epoxy is within the range of 10,000 to 100,000.
The above polyglycidyl ether can be obtained from polyoxy alkylene glycol diglycidyl ether having a molecular weight of 500 to 1,000 and a polycyclic phenol compound. A dicarboxylic acid containing a long chain alkyl group can be added to the above two reactants. The above polyoxyalkyleneglycol diglycidyl ether may be polyoxypropyleneglycol diglycidyl ether and the above polycyclic phenol compound is bisphenol A. The above dicarboxylic acid containing a long chain alkyl group is a dimer acid. In addition, the present invention provides a cationic electrodeposition paint composition comprising a flexible resin comprising the above amino-polyether-modified epoxy, an amine-modified epoxy resin and a blocked polyisocyanate curing agent, for example the above amine-modified epoxy resin contains an oxazolidone ring.
An amino-polyether-modified epoxy of the present invention is characterized in that it is obtained by reacting amino polyether represented by a formula as follow: 
wherein m is an integer of 2 or more, R is hydrogen, methyl group or ethyl group, and n is 2 or 3,
with polyglycidyl ether having a molecular weight of 1,000 to 7,000 and an epoxy equivalent of 500 to 3,500, wherein an equivalent ratio of a primary amino group of the above amino polyether to an epoxy group of the above polyglycidyl ether is controlled within the range of 0.52 to 1.0.
The above amino polyether can be obtained by adding alkylene oxide to monoethanol amine.
The above amino polyether, as represented by the above formula, has a polymethylene chain which has a primary amino group at one end and has a polyoxyalkylene chain having a terminal hydroxy group at the other end.
In the formula, m shows number of repeating units of polyoxyalkylene chain, which is preferably an integer from 5 to 25, more preferably an integer from 10 to 25. R in a polyoxyalkylene chain is preferably hydrogen or methyl group. In addition, R is usually the same, but may be two types or more. In the above formula, n represents number of repeating units of polymethylene chain bonding to a primary amino group and generally is 2 or 3, but 2 is more suitable.
The above polyglycidyl ether used in the present invention has a molecular weight of 1,000 to 7,000 and an epoxy equivalent of 500 to 3,500.
If polyglycidyl ether has a molecular weight of less than 1,000 and/or an epoxy equivalent of less than 500, an electrodeposited coating formed with a cationic electrodeposition paint containing an amino-polyether-modified epoxy obtained by using the polyglycidyl ether does not provide with sufficient flexibility. On the other hand, if polyglycidyl ether has a molecular weight of more than 7,000 and/or an epoxy equivalent of more than 3,500, adhesion between the electrodeposited coating and an intermediate-coated or a top-coated coating coated thereon decreases.
The above polyglycidyl ether compound can be obtained by reacting polyoxy alkylene diglycidyl ether having a molecular weight of 500 to 1,000 with a polycyclic phenol compound. The polyglycidyl ether compound can preferably be polyoxy alkylene glycol diglycidyl ether, which includes polyoxyethyleneglycol diglycidyl ether (epoxy ether of polyethylene glycol), polyoxypropyleneglycol diglycidyl ether, polyoxyisopropyleneglycol diglycidyl ether, polyoxybutyleneglycol diglycidyl ether and the like. Especially, polyoxyisopropyleneglycol diglycidyl ether is preferable.
The polyoxyalkyleneglycol diglycidyl ether preferably has a molecular weight of 500 to 1,000. If the molecular weights are less than 500, the resulting electrodeposited coating leads to decrease of impact resistance, and if the molecular weights are more than 1,000, adhesion with an intermediate-coated or a top-coated coating is defective.
The polycyclic phenol compound used herein can be one that used as a component in synthesis of an amine-modified epoxy resin that is a binder component in a general cationic electrodeposition paint composition. To be specific, it includes bisphenol A, bisphenol F, bisphenol S, phenol novolak cresol novolak, and the like. Especially, bisphenol A is preferable.
A molecular weight of the above polyglycidyl ether can be controlled by adjusting a formulating amount of the above polyoxy alkylene glycol diglycidyl ether and the above polycyclic phenol compound.
If necessary, the molecular weight can be also controlled by formulating a suitable amount of a dicarboxylic acid containing a long chain alkyl group. Examples of the dicarboxylic acids include 1,10-dodecane dicarboxylic acid, adipic acid and the like, especially, a dimer acid (available as, Barsadime 216) being preferable.
When the above thee components are polyoxyisopropyleneglycol diglycidyl ether, bisphenol A and dimer acid (available as, Barsadime), a formulating ratio can be controlled in 60 to 90/5 to 30/0 to 30 by weight to obtain a polyglycidyl ether having an objective molecular weight.
The amino-polyether-modified epoxy of the present invention is obtained by reacting the above amino polyether with the above polyglycidyl ether. When these two compounds are reacted, it is required that an equivalent ratio of a primary amino group of the above amino polyether to an epoxy group of the above polyglycidyl ether is controlled within the range of 0.52 to 1.0. If an equivalent ratio is less than 0.52, the resulting amino-polyether-modified epoxy keeps a portion of epoxy groups unreacted at an end of its molecule and proceeds polymerization to result in gellationl. On the other hand, if an equivalent ratio is more than 1.0, the resulting epoxy has a low molecular weight and an amino polyether remains therein to decrease stability of paint.
The amino-polyether-modified epoxy of the present invention preferably has a molecular weight of 10,000 to 100,000. If an amino-polyether-modified epoxy has a molecular weight of less than 10,000, an electrodeposited coating obtained by using it has poor impact resistance, while if an amino-polyether-modified epoxy has a molecular weight of more than 100,000, appearance of an electrodeposited coating is aggravated and adhesion of the electrodeposited coating with an intermediate-coated or a top-coated coating coated thereon decrease. In addition, the high molecular weight leads to high viscosity, and does not sufficiently perform a function as a reactive diluent, which results in incapability of reducing an amount of solvent to be used.
Then a method for synthesizing the amino-polyether-modified epoxy of the present invention will be explained.
The reaction of polyoxyalkyleneglycol diglycidyl ether with polycyclic phenol can be carried out by a art-known method generally used in synthesis of an epoxy resin. For example, a predetermined amount of polyoxyalkyleneglycol diglycidyl ether and a phenol compound are poured in a reaction vessel and heated with stirring, to which a catalyst, such as benzyl dimethyl amine, 2-ethyl-4-methyl-imidazole and the like, is added to proceed a reaction, or if necessary, a dicarboxylic acid containing a long chain alkyl group to adjust a molecular weight, such as a dimer acid and the like, is added and reacted together to obtain polyglycidyl ether. A predetermined amount of amino polyether is then added and heated again to react with the polyglycidyl ether obtained above, thus obtaining the amino-polyether-modified epoxy of the present invention.
Then, a cationic electrodeposition paint of the second embodiment of the present invention will be specifically explained.
The cationic electrodeposition paint composition of the present invention comprises a flexible resin composed of the above amino-polyether-modified epoxy, an amine-modified epoxy resin and a blocked polyisocyanate curing agent.
The amine-modified epoxy resin can be one that has been used in cationic electrodeposition paint. Some of the resins are explained in Japanese Patent Publication Nos. 55-34238, 56-34186 and 59-15929. It is preferably used that the above amine-modified epoxy resin has a molecular weight of 600 to 8,000, an amine value of 16 to 230 and an epoxy equivalent of 300 to 4,000.
These amine-modified epoxy resins can be produced by ring-opening all epoxy rings of a bisphenol type epoxy resin with an active hydrogen compound which can introduce a cationic group, or by ring-opening a portion of epoxy rings with another active hydrogen, of which remaining epoxy rings are reacted with an active hydrogen compound which can introduce a cationic group.
A typical example of the above bisphenol type epoxy resin is bisphenol A type or bisphenol F type epoxy resin. Bisphenol A type epoxy resins are commercially available, including Epycoat 828 (available from Yuka Shell Epoxy Co., epoxy equivalent of 180 to 190), Epycoat 1001 (available from Yuka Shell Epoxy Co., epoxy equivalent of 450 to 500), Epycoat 1010 (available from Yuka Shell Epoxy Co., epoxy equivalent of 3,000 to 4,000) and the like. Bisphenol F type epoxy resins are also commercially available, including Epycoat 807 (available from Shell Epoxy Petrochemical Corporation, epoxy equivalent of 170) and the like.
The active hydrogen compound which can introduce a cationic group includes primary amine and secondary amine. Examples thereof include butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, monoethanolamine, diethanolamine and N-methylethanolamine and a secondary amine with a ketiminized primary amine, such as a ketimine of amino ethyl ethanol amine or diketimine of diethylene triamine. These amines may be used in combination.
The other active hydrogen compound which can be used for ring-opening an epoxy ring includes monophenols, such as phenol, cresol, nonylphenol and nitrophenol; monoalcohols, such as hexyl alcohol, 2-ethylhexanol, stearyl alcohol and monobutyl- or monohexyl-ether of ethylene glycol or propylene glycol; aliphatic monocarboxylic acids, such as stearic acid and octyric acid; aliphatic hydroxyl carboxylic acids, such as hydroxyl pivalic acid, lactic acid and citric acid; and mercaptoalkanols, such as mercaptoethanol.
The amine-modified epoxy resin is preferably an epoxy resin containing an oxazolidone ring in a backbone of the resin as disclosed in Japanese Laid-Open Patent Application Nos.5-306327, 6-329755 and 7-33848. Details of the above amine-modified epoxy resin containing an oxazolidone ring will be explained hereinafter.
It is known that a bifunctional epoxy resin is reacted with a diisocyanate compound blocked with a monoalcohol, i.e. bisurethane, to obtain a chain-extended epoxy resin containing an oxazolidone ring. An epoxy group of the chain-extended epoxy resin is ring-opened with an amine to obtain an amine-modified epoxy resin, which is one of amine-modified epoxy resin containing an oxazolidone ring. In addition, by the method as disclosed in the above Japanese Laid-Open Patent Application No. 7-33848, one isocyanate group of a diisocyanate compound is reversibly blocked with a monoalcohol and the other isocyanate group is irreversibly blocked with a compound containing a hydroxyl group to obtain an asymmetric bisurethane compound, which is reacted with bifunctional epoxy resin to obtain an modified epoxy resin containing an oxazolidone ring. An epoxy ring of the modified epoxy resin thus obtained is ring-opened with an active hydrogen compound that can introduce a cationic group, such as amine, to obtain a cationic modified epoxy resin.
In the above method, the hydroxyl compound which irreversibly blocks the one isocyanate group of the diisocyanate compound includes an aliphatic monoalcohol having 4 or more carbon atoms, such as butanol, 2-ethyl hexanol and the like; a long chain phenol, such as nonyl phenol; a glycol monoether, such as mono-2-ethyl hexyl ether of ethylene glycol or propylene glycol.
A blocked polyisocyanate curing agent contained in the cationic electrodeposition paint composition of the present invention is generally used in the art, and may generally be obtained by blocking a polyisocyanate. Examples of the polyisocianates are tolylene diisocyanate (TDI), 4,4xe2x80x2-diphenylmethane diisocyanate (MDI), xylene diisocyanate (XDI) and the like; an aliphatic or alicyclic diisocyanate compound, such as hexamethylene diisocyanate (HMDI), isophorone diisocyanate (IPDI), 2,5- or 2,6-bis (isocyanato methyl) bicyclo [2,2,1] heptane (NBDI) and the like; a dimer or trimer of the diisocyanate compound or one obtained by adding trimethylol propane to the diisocyanate compound.
A blocking agent used in the above blocked polyisocyanate curing agent is one that is attached to an isocyanate group to be stable at room temperature, but can dissocate to reproduce a free isocyanate group when heating above a dissociation temperature.
Concrete examples of the blocking agents are phenol type blocking agents, such as phenol, cresol, xylenol, chlorophenol and ethylphenonl; lactam type blocking agents, such as xcex5-caprolactam, xcex4-valerolactam, xcex3-butyrolactam and xcex2-propiolactam; active methylene type blocking agents, such as ethyl acetoacetate and acetyl acetone; alcohol type blocking agents, such as methanol, ethanol, propanol, butanol, amylalcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, benzyl alcohol, methyl glycolate, butyl glycolate, diacetone alcohol, methyl lactate and ethyl lactate; oxime type blocking agents, such as formaldoxime, acetoaldoxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime and cyclohexaneoxime; mercaptan type blocking agents, such as butylmercaptan, hexylmercaptan, t-butylmercaptan, thiophenol, methyl thiophenol and ethyl thiophenol; acid amide type blocking agents, such as amide acetate and benzamide; imide type blocking agents, such as imide succinate and imide maleate; imidazole type blocking agents, such as imidazole and 2-ethyl imidazole; and the like. When curing at low temperature of 160xc2x0 C. or less is required, lactam type and oxime type blocking agents are preferably used.
The cationic electrodeposition paint composition of the present invention is obtained by dispersing the flexible resin comprising the amino-polyether-modified epoxy, the amine-modified epoxy resin and the blocked polyisocyanate curing agent as mentioned above in an aqueous medium containing a neutralizer. When the above amino-polyether-modified epoxy is used as a flexible resin that is a component of a cationic electrodeposition paint composition, it is necessary that a neutralizer and ion-exchanged water are added to the amino-polyether-modified epoxy and stirred sufficiently to obtain a form of emulsion.
The neutralizer is not limited as long as it has been generally used in the production of cationic electrodeposition paint, but including inorganic acid or organic acid, such as hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid and lactic acid. The neutralizer is used in such an amount that it partially neutralizes amino groups in the above amino-polyether-modified epoxy to form an aqueous dispersion.
In order to keep stable the emulsion of an amino-polyether-modified epoxy thus obtained above, an amine value of the amino-polyether-modified epoxy is preferably contorolled to 32 meq or more per a solid content of 100 g. If the amino-polyether-modified epoxy has an amine value of less than 32 meq, its water dispensability decreases.
The cationic electrodeposition paint composition of the present invention usually contains a pigment-dispersed paste in addition to the flexible resin, the amine-modified epoxy resin, the blocked polyisocyanate curing agent and the neutralizer as mentioned above. The pigment-dispersed paste is prepared by dispersing a pigment together with a pigment-dispersing resin in an aqueous medium.
The above pigment is not limited especially if it is usually used, and includes color pigments, such as titanium white, carbon black and red oxide; filler pigments, such as kaolin, talc, aluminum silicate, calcium carbonate, mica, clay and silica; corrosion resistant pigments, such as zinc phosphate, iron phosphate, aluminum phosphate, calcium phosphate, zinc phosphite, zinc cyanide, zinc oxide, aluminum tripolyphosphate, zinc molybdate, aluminum molybdate, calcium molybdate and aluminum phosphorus molybdate.
As the above pigment-dispersing resin, a cationic or nonionic surfactant having a low molecular weight or a modified epoxy resin having a quaternary ammonium group and/or a tertiary sulfonium group is generally used.
After given amounts of the resin for dispersing a pigment and the pigment as mentioned above are mixed, the pigment is dispersed in the resin using usual dispersion equipment, such as a ball mill and grind mill until the pigment in the mixture has a uniform and given particle size to obtain a pigment-dispersed paste.
More concretely, given amounts of the amine-modified epoxy resin and the blocked polyisocyanate curing agent as mentioned above are uniformly mixed, and the mixture is dispersed in an aqueous medium containing a neutralizer to obtain an emulsion (referred to as xe2x80x9cmain emulsionxe2x80x9d hereinafter) of a mixture of the amine-modified epoxy resin and the blocked polyisocyanate curing agent. On the other hand, separately, the above flexible resin is made to an emulsion (referred to as xe2x80x9cflexibility-providing emulsionxe2x80x9d hereinafter) by a similar method (described as emulsion provided with flexibility as follow). The above main emulsion, the flexibility-providing emulsion, the above pigment-dispersing paste and ion-exchanged water are mixed in suitable amounts to obtain the cationic electrodeposition paint of the present invention.
However, the method for forming the emulsions of the above flexible resin, the above amine-modified epoxy resin and the above blocked polyisocyanate curing agent are not limited to those as mentioned above. For another example, the above three components may be separately emulsified or all of the three components may be mixed together and then emulsified.
The above flexible resin of the present invention is preferably added within the range of 1 to 30 weights % based on total solid resin contents in the cationic electrodeposition paint composition. If an amount is less than 1 weight %, an electrodeposited coating is provided with insufficient flexibility and a solvent amount does not reduce effectively. On the other hand, if an amount is more than 30 weights %, the corrosion resistance of an electrodeposited coating would be deteriorated.
An amount of the above blocked polyisocyanate curing agent may be enough to react with a functional group having an active hydrogen, such as amino group and hydroxyl group in the above amine-modified epoxy resin to provide an excellent cured coating when curing. It is therefore general that a weight ratio of a solid content of the above amine-modified epoxy resin to a solid content of the above blocked polyisocyanate curing agent is within the range of 90/10 to 50/50, preferably 80/20 to 65/35.
The above blocked polyisocyanate curing agent is also reacted with a hydroxyl group in the above flexible resin, but the above amount can be enough to react with the hydroxyl group.
The above pigment-dispersed paste is formulated in such an amount that a weight ratio of the above pigment to a total solid content of the resins in a cationic electrodeposition paint is within the range of 1 to 35%.
The cationic electrodeposition paint of the present invention can contain tin compounds, such as dibutyltin dilaurate and dibutyltin oxide or a usual urethane cleavage catalyst. An amount thereof is preferably within the range of 0.1 to 5.0 weights % based on the above blocked polyisocyanate curing agent.
The cationic electrodeposition paint of the present invention may contain conventional additives for paint, such as water-miscible organic solvent, surfactant, antioxidant, ultraviolet-absorbent and the like.